1. Field of the Invention
The present invention relates to a semiconductor device, a display device, or a light-emitting device, or a driving method thereof.
2. Description of the Related Art
Flat panel displays such as liquid crystal displays (LCD) become widely used in recent years. However, LCDs have various drawbacks such as a narrow viewing angle, narrow chromaticity range, and slow response speed. Thus, to overcome those drawbacks, research of an organic EL (also referred to as an electroluminescence, an organic light-emitting diode, an OLED, or the like) displays have been actively conducted (Patent Document 1).
However, organic EL displays have a problem in which current characteristics of transistors for controlling current which flows into organic EL elements vary from pixel to pixel. When current flowing into the organic EL elements (that is, current flowing into the transistors) varies, luminance of the organic EL elements also varies, whereby display screens display images with unevenness. Thus, methods for compensating variation in threshold voltage of transistors have been examined (Patent Documents 2 to 6).
However, even if variation in the threshold voltage of the transistors is compensated, variation in mobility of the transistors also leads to variation in current flowing into an organic EL element, so that image unevenness occurs. Thus, methods for compensating not only the threshold voltage but also variation in mobility of transistors have been examined (Patent Documents 7 and 8).